A microphone is a transducer that converts sound into an electrical signal. Several different types of microphone are in use, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. The most common are the dynamic microphone, which uses a coil of wire suspended in a magnetic field. A condenser microphone uses the vibrating diaphragm as a capacitor plate. A piezoelectric microphone uses a crystal of piezoelectric material. Examples of microphones also include a digital microphone.